1. Field of the Invention
The present invention relates to a thin film magnetic head including a magnetoresistive element and a method of manufacturing the same, and also relates to a magnetic head slider, head gimbal assembly, head arm assembly and magnetic disk device including the thin film magnetic head.
2. Description of the Related Art
A thin film magnetic head, which includes a magnetoresistive element (MR element) exhibiting the magnetoresistive effect (MR effect), is widely used for reading out data written on magnetic recording media such as a hard disk. Recently, a thin film magnetic head which includes a giant magnetoresistive element (GMR element) exhibiting the giant magnetoresistive (GMR) effect is more general because of the highly-progressed recording density of the magnetic recording medium. Examples of such GMR element include a spin valve GMR element (SV-GMR element).
This SV-GMR element is configured in such a manner that a magnetic layer in which its magnetization direction is fixed in a given direction (magnetically pinned layer) and a magnetic layer in which its magnetization direction is varied in accordance with an external signal magnetic field applied from outside (magnetically free layer) are stacked via a nonmagnetic interlayer. In particular, those configured to make a read current flow in a direction along a stacking plane of the element during a reading operation is called CIP-GMR element (Current in Plane GMR element). Further, a thin film magnetic head including the CIP-GMR element is called CIP-GMR head. In this configuration, electric resistance (namely, voltage) is varied when the read current is applied in accordance with a relative angle between the magnetization directions of the two magnetic layers (the magnetically pinned layer and the magnetically free layer).
Recently, to comply with further improvement in the recording density, CPP (Current Perpendicular to the Plane)-GMR head, which includes a CPP-GMR element in which the read current flows in a direction orthogonal to the staking plane at the time of reading operation, has been developed. Such CPP-GMR head generally includes a GMR element, a pair of magnetic domain controlling layers that are arranged to face each other in a track-width direction with the GMR element in between via an insulating layer, and a bottom electrode and a top electrode that are arranged to face each other with the GMR element and the pair of magnetic domain controlling layers in between in the stacking direction. The magnetic domain controlling layers control the magnetic domain of a magnetically free layer so to align the magnetic domain of the magnetically free layer to a single domain by applying a bias magnetic field to the magnetically free layer in the GMR elements, thereby stabilization of the magnetization direction is attained. The top and bottom electrodes also serve as top and bottom shielding films. Such CPP-GMR head recognizes advantages in that high power is available when reducing the dimension in a read track width direction compared with the CIP-GMR head. Namely, in the CIP-GMR head, since the read current flows along the in-plane direction, dimensional reduction in the read track width direction results in the narrowing of magnetic sensitive area through which the read current passes, thereby decreasing the amount of voltage changes. On the other hand, since the read current passes in the stacking direction in the CPP-GMR head, the dimensional reduction in the read track width direction does not affect the amount of voltage changes. For this reason, the CPP-GMR head is advantageous compared with the CIP-GMR head in terms of the reduction of track density whose unit is TPI (number of tracks per inch). What is more, since insulating layers are omitted between the CPP-GMR element and top/bottom shielding layers, that allows the reduction, by the thickness of the omitted layers, of the linear recording density, whose unit is BPI (bit per inch), as compared with the CIP-GMR head.
There is also a tunnel MR element (TMR element) which is configured similar to the CPP-GMR element in that the read current flows in a direction orthogonal to the in-plane direction. This TMR element includes an ultra-thin insulating layer called tunnel barrier layer so as to obtain much higher resistance change ratio than that of the above-mentioned CPP-GMR element. For this reason, the thin film magnetic head including the TMR element (TMR head) is highly expected to comply with the further improvement in the recording density.
In the thin film magnetic head including an element such as CPP-GMR element and TMR element, to comply with the further improvement in the linear recording density, it is necessary to improve the read resolution for a reading waveform obtained from a magnetic recording medium. For that purpose, thickness of the GMR element (TMR element) and the pair of magnetic domain controlling layers need to be reduced so that the distance between the top shielding layer and the bottom shielding layer, i.e., the read gap, may be decreased. However, there is a problem that if the thickness of the GMR element (TMR element) and the magnetic domain controlling layers is reduced, the leakage ratio of the bias magnetic fields, which is leaked out from the magnetic domain controlling layers to the top and bottom shielding layers, increases so that it becomes difficult to apply enough bias magnetic field to the magnetically free layer.
Accordingly, as shown in Japanese Patent Application Publication No. 2008-41675 (JP2008-41675A) or Japanese Patent Application Publication No. 08-45035 (JP08-45035A), for example, a thin film magnetic head with a trilaminar magnetic domain controlling layer, in which a magnetic bias layer typically made of a ferromagnetic material such as cobalt platinum alloy (CoPt) is sandwiched between a buffer layer and a cap layer typically made of chromium (Cr), has been proposed. With such configuration, it seems possible for the thin film magnetic head to apply enough bias magnetic field to a magnetically free layer even if the thickness of the magnetic domain controlling layer is reduced, because coercive force naturally held in the magnetic domain controlling layer can be kept with little leakage.